High Definition Digital TV
The launch of HDTV or high def television represents the most important development in the specification of broadcasting and TV ever since colour. For a flat panel widescreen tv to receive and benefit from a high definition signal it must have a screen resolution of 1280 X pixels 720 pixels and be labelled HD Ready.
What does ‘HD ready’ mean ?
Any television that is HD Ready is capable of receiving and displaying a high definition picture. To meet this specification the TV should have a picture resolution of at least 1280 x 720 pixels. They have got to be able to accept a signal that is 1080i/25 or 720p/50, where the 1080 or 720 is the number of vertical lines, the ‘i’ is for an interlaced picture and the ‘p’ is for a progressive scan picture, and the 25 and the 50 are the number of frames displayed each second. In addition the televisions must have either DVI or HDMI and Component signal input connectors.
For a 1366 x 768 pixels HD ready TV, if it receives a 1080i signal then scalers inside the flat screen tv will down convert the image to fit the 768 lines flat screen tv. This is done via complex algorithm sequences in the scaler which systematically crops the picture down to the resolution of the panel. If the signal is at 720p it follows that the signal will be slightly upscaled to fill the 768 vertical lines using complicated algorithms.
If a HD Ready tv receives a full HD signal of resolution 1920 x 1080 pixels the picture signal has to be interpolated or converted down to display the image. One to one mapping of the pixels is not possible.
What is ‘HD ready 1080P’ ?
Any Television that carries the ‘HD ready 1080p’ is naturally capable of displaying a ‘full’ 1080P signal with adequate pixels to offer true pixel-for-pixel mapping with no interpolation. A HD ready 1080p flat panel television has a screen resolution of (1920 pixels x1080 pixels) i.e. 1080P, where ’1080′ is the vertical resolution of the image and the ‘P’ is for Progressive scan. HD ready 1080P is the maximum resolution available in the UK on HD televisions hence the ‘full’ term. These sets can display 1080p and 1080i images without distortion i.e. with 1:1 pixel mapping. They also boast HDMI or DVI HD input at 1080p HD and display signals that are at either 24 or 50 frames per second.
If a flat screen 1080P TV receives a 720P picture the signal is ‘oversampled’ to suit the resolution of the 1080P widescreen TV. This is completed using extremely complex algorithm sequences.
Full HD tv – What is it ?
Early high definition tv’s didn’t have the ‘HD Ready 1080p’ logo and may well not be compatible with this specification and may not show selected signal inputs.
Interlaced or Progressive
Interlaced picture have two fields that are alternated to make up a frame where every other line is shown on each frame. Thus the odd lines are on one field and the even lines are on the other field. When the two fields containing the odd and even lines are shown successively for each frame at twice the frame rate this is known as Interlacing.
When a image is interlaced, moving images on video appear to have smoother movement for the reason that each field of the frame are shot at different times. The system of picture interlacing was in the first place used to enhance the quality of the picture on tube televisions using the equivalent amount of bandwidth for the broadcast signal.
In the UK PAL tvs operates at 25 frames a second with 50 fields a second. A broadcasted signal that is Interlaced requires half the signal bandwidth of a Progressive signal. A progressive signal has a scan rate of 50 full frames per second compared with an interlaced signal which has half the frame speed.
CRT (Cathode Ray Tube) television or the old CRT TVs are able to show interlaced images made for television or on a video camera since they have an electron scan. Flat panel lcd tvs and plasma tvs aren’t able to show such signals without the use of progressive scanning or deinterlacing.
Progressive scan delivers benefits.
This is a method to display, transmit, and store a moving image. Every frame has all of the lines instead of even lines or odd lines as with an Interlaced signal and they are displayed in sequence.
Progressive scan has the benefit of superior vertical resolution than interlaced images with the same frame rate and no interlace artifacts or blurring, and therefore less eye strain. Also better results are possible for scaling to higher resolutions than the comparable interlaced sources. For the best scaling results full frames work the best whereas interlaced video sources have got to be deinterlaced prior to being scaled and this can cause very noticeable combing artifacts.
What is the difference between the 720p/50 and 1080i/25 formats?
On static images a 1080i/25 (1920 x pixels 1080 pixels) produces a a little higher horizontal picture resolution than a 720p/50 (1280 X pixels 720 pixels) picture. Moving pictures on an interlaced picture have a lower subjective line resolution because of line twitter or artifacts caused by the fields being somewhat dissimilar that create a frame. Broadcasters tend to opt for 1080i/25 over 720p/50 since it requires a reduced amount of bandwidth, but both systems are used for HD TV broadcasts.
Progressive scanning 720p gives more fluid motion, especially on slow-motion, than an interlaced 1080i signal. Whereas interlaced 1080i signals give better static resolution. If the internal processing is competent enough a 1080i signal on a 1080 display will still look better than the 720p material. The best one depends on whether you are to display more static pictures or more moving pictures and what is more important to you.
The conversion of a progressive source such as 1080p/50 into an interlaced configuration such as 1080i/25 is easier than the conversion of an interlaced signal to a progressive format.
What is 1080p/24 ?
The ultimate picture quality is obtainable on films with a 1080p signal at 24 frames per second, when viewed via a BlueRay player on a flat panel high def tv. The frame rate of 24 per second is identical to the original cinema film instead of being increased to 25 frames per second. The internal circuitry in the TV produces extra middle frames so that the frame rate is increased to 48 or 72 producing smoother on screen movement.
Sources of high def.
All HD tv broadcasts are currently at either 720p/50 or 1080i/25 and are can be viewed to their full benefit on HD Ready widescreen tvs. At present the only broadcasters of high def. TV are by satellite on Freesat and Sky digital hd, and over the internet on BT vision, and on cable by Virgin media. The only sources of Full HD 1080p are either by download on the web and on Blueray. The Xbox 360 can give a 720p/50 image for video gamesand the Playststion 3 can create a 1080p image for games.
The conclusion
High definition enhances the viewing experience and makes television more engaging. If you don’t propose to use a Blueray player, Playstation 3, or to download films from the webthen a HD ready tv will probably suffice. On the other hand if you need to future proof yourself against the likelihood of future full high definition 1080p broadcasts then the full HD 1080p models are the ones to buy. Clearly, if you already possess, or are going to buy a Blueray player, Playstation 3 or to you are going to down load full high definition films then the full HD 1080p tv is the logical choice.
Tags: LIVE TV
